Visual impairment, or vision impairment, refers to the vision loss of an individual to such a degree as to require additional support for one or more aspects of their life. Such a significant limitation of visual capability may result from disease, trauma, congenital, and/or degenerative conditions that cannot be corrected by conventional means, such as refractive correction, such as eyeglasses or contact lenses, medication, or surgery. This degree of functional vision loss is typically defined to manifest with:                a corrected visual acuity of less than 20/60;        a significant central visual field defect;        a significant peripheral field defect including bilateral visual defects or generalized contraction or constriction of field; or        reduced peak contrast sensitivity in combination with any of the above conditions.        
However, in the United States and elsewhere, more general terms such as “partially sighted”, “low vision”, “legally blind” and “totally blind” are used to describe individuals with visual impairments rather than quantified visual acuity. As human brain-eye combination is fundamental to how we perceive and interact with both the real and virtual worlds any degradation may have significant impact to the individual's quality of life. Whilst there are many components of the human eye and brain that impact perception, vision, stability, and control only a few dominate the path from eye to the optic nerve and therein to the brain, namely the cornea, lens, vitreous body, and retina. For age groups 12-19, 20-39, and 40-59 within the United States approximately 93%, 90%, and 92% of visual impairments can be corrected by refractive means.
Such refractive means include eyeglasses, contact lenses, and laser surgery and are normally used to correct common deficiencies, namely myopia, hyperopia, astigmatism, and presbyopia by refractive corrections through the use of concave, convex, and cylindrical lenses. However, within the age grouping 60+ this ability to correct visual impairments drops significant to approximately 60%. In fact, the ability to employ refractive corrections drops essentially continuously with increasing age as evident from Table 1 below.
TABLE 1Dominant Vision Disorders That Cannot beAddressed with Refractive Correction40-4950-5960-6970-7980+Intermediate Macular2.0%3.4%6.4%12.0% 23.6%DegenerationAdvanced Macular Degeneration0.1%0.4%0.7%2.4%11.8%Glaucoma0.7%1.0%1.8%3.9% 7.7%Low Vision (from all causes)0.2%0.3%0.9%3.0%16.7%40-4950-6465-7475+Diabetic Retinopathy1.4%3.8%5.8%5.0%
Amongst the eye disorders that cannot be addressed through refractive correction include retinal degeneration, albinism, cataracts, glaucoma, muscular problems that result in visual disturbances, corneal disorders, diabetic retinopathy, congenital disorders, and infection. Age-related macular degeneration for example, currently affects approximately 140 million individuals globally and is projected to increase to approximately 180 million in 2020 and 208 million in 2030 (AgingEye Times “Macular Degeneration Types and Risk Factors”, May 2002 and United Nations “World Population Prospects—2010 Revision”, June 2011). Additionally, visual impairments can arise from brain and nerve disorders, in which case they are usually termed cortical visual impairments (CVI).
Accordingly, it would be evident that a solution to address non-refractive corrections is required. It would be further evident that the solution must address multiple disorders including, but not limited to those identified above, which manifest uniquely in each individual. For example, myopia, shortsightedness, corrected refractively with lenses is achieved through providing a concave lens of increasing strength with increasing myopia and accordingly a single generic lens blank can be machined to form concave lenses for a large number of individuals suffering from myopia or if machined to form convex lenses those suffering hyperopia. In contrast, macular degeneration will be unique to each individual in terms of the regions degenerating and their location. It would therefore be beneficial to provide a solution that corrects for visual impairments that cannot be corrected refractively that is customizable to the specific requirements of the user. Further, it would beneficial for the correction to account for varying requirements of the user according to their activities and/or context of their location as provided for example by bifocals or progressive bifocal lenses with refractive corrections.
Accordingly, the inventors have invented a head-worn or spectacle-mounted display system which derives its image source from a video camera mounted similarly, wherein the optical characteristics of the camera system, the display system and possibly even the video file format, are designed to match with the individual's visual impairment be it through retinal performance, nervous disorder, and/or higher order processing disorder. Typically, such a system would take advantage of the wearer's natural tendency to position their head/neck, and therefore the camera, so that an object of interest is positioned in the preferred location in the display. This is most commonly in the center of the display Field of View (FOV) but can be eccentrically located in some cases to avoid blind spots such as caused for example by Macular Degeneration or other visual diseases as described above.
There are several potential advantages to a system that closely matches the characteristics of human visual behavior and performance in this way. The design and selection of optical components could be optimized for very high performance near the center, most accurate regions of the human vision system, with significantly relaxed performance specifications at the periphery of the same. Alternatively, the performance may be optimized for non-central regions of the human vision system or to exploit physiological and psychological characteristics of the individual's vision system.
It would be further beneficial where the head-worn or spectacle mounted video display system presents the video to the individual's eye in a manner wherein it is intentionally altered to take advantage of the natural physiological behavior of the entire human vision system from the retinal photoreceptors and nerve cells through the occipital lobe and cerebral cortex. The video presented to the individual's eye may be modified spectrally, spatially and/or temporally to improve the individual's perception and functional vision.
Accordingly, due to the competing requirements of processing the received image content to present to the user in a format enhancing their vision and providing the image content at rates compatible with their activities and hence close to real time, it would beneficial for aspects of the system to be implementable in formats and designs allowing tradeoffs to be made. Accordingly, in some embodiments of the invention image content file formats, and the transmission of this data through the system, are modified to provide improvements for multiple competing aspects of a head-worn or spectacle mounted video display system including parameters including, but not limited to, power consumption, video frame rate, latency, and acuity etc. Likewise, elements of the optical system may be adjusted according to similar competing parameters as well as considering additional aspects including, but not limited to, cost, patient optical characteristics, and human vision characteristics.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.